Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

In southern New Zealand, grazing of forage crops is common practice to satisfy feed requirements of animals in winter when pasture growth is limited. This practice has been shown to cause soil physical damage and increased loss of surface water contaminants sediment and phosphorus (P) to water bodies. Strategies to mitigate the loss of sediment and P were trialled on a Pallic soil type (Aeric Fragiaquept) in the North Otago Rolling Downlands of New Zealand. All sites were irrigated and measurements were made of losses in overland and sub‐surface flow from intensive cattle or sheep grazed, winter forage crops, and sheep grazed pasture. Two mitigations (restricted grazing of crop to three hours and the application of aluminium sulphate) were assessed for their potential to decrease contaminant loss from cropland. Volumes of surface runoff and loss of total P, filterable reactive P and sediment showed significant differences (P < 0.05) between the control treatments (i.e. no mitigation) with cattle crop (88 mm surface runoff) > sheep crop (67 mm) > sheep pasture (33 mm). The contribution of irrigation water to overland flow water, as a result of saturation‐excess conditions, varied between treatments with more loss under cattle crop (20% of total) compared with sheep crop (15%) and sheep pasture (11%). These differences are probably an effect of soil physical condition and highlight the importance of accurate irrigation scheduling to keep soil moisture below field capacity. Restricted winter grazing and alum application after grazing significantly (P < 0.05) decreased P losses in surface runoff under cattle (from 1.4 to 0.9 kg P/ha) and sheep (from 1.0 to 0.7 kg/P/ha) grazed crop plots by about 30%. In cattle grazed plots, restricted grazing also decreased suspended sediments (SS) by 60%. The use of restricted grazing is suggested as a means of decreasing P and SS loss from grazed winter forage crops. The use of alum shows some promise for decreasing P losses, but requires further work to determine its long‐term effectiveness and use in other soils and management regimes.     

Excessive application of nitrogen and phosphorus fertilizers induces soil acidification and phosphorus enrichment during vegetable production in Yangtze River Delta,China

Intensive vegetable cultivation has developed very rapidly in China, and investigation of current soil nutrient problems in vegetable fields and their potential environmental risk is important for local soil nutrient management strategies. Three hundred and sixty‐six soil samples were collected from greenhouse vegetable fields, open vegetable fields and rice/wheat rotation fields in southern Jiangsu Province, the most intensive vegetable‐producing areas in Yangtze River Delta, China, for the analysis of their soil fertility status. Soil acidification and P enrichment were the main problems identified in this area of vegetable production, with about 20 and 17% of the open and greenhouse vegetable field soils, respectively, being extremely acid with soil pH values below 5.0. In contrast, no soils under rice/wheat rotation fields were as acidic. Percentages of sites with Olsen‐P concentrations < 90 mg/kg were 61, 85 and 0% for soils growing greenhouse vegetable, field vegetable and rice/wheat, respectively. The nitrogen (N) surplus for vegetable fields exceeded 170 kg/ha/crop, and the phosphorus (P) surplus exceeded 40 kg/ha/crop. Thus, current vegetable production leads to potential environmental risks of N and P pollution of nearby aquatic bodies. Insufficient supplementation with potassium fertilizers was found in some vegetable fields. Several ameliorative measures are proposed.     

Sediment and Phosphorus Loads from a Stream Draining Agricultural and Forest Lands in Northwest Spain

ABSTRACT

Transport of suspended sediment (SS) and phosphorus (P) via surface runoff from soils to surface waters is a major problem of water quality degradation in many European rivers and in other parts of the world. This problem is especially serious during wet periods, which can produce twice the P loads of dry periods. In this study, the SS load and particulate phosphorus (PP) exported from a small catchment located in NW Spain (in which cultivated soils had different degrees of vegetation cover) were analyzed during two rainy periods of February 2006 and February 2007. The SS and PP loads were calculated from the data of discharge, and SS and PP concentrations were measured in water samples collected at the catchment outlet. SS and PP loads were higher in 2006 than in 2007, while there was higher rainfall and stream flow in 2007. Differences in the degree of vegetation cover in the cultivated fields with good connectivity with the stream, which was the main source area of sediment in this catchment, explain the differences in SS and PP loads between the two periods. Soil losses caused during both rainy periods were low (0.02 Mg ha^?1); however, they may be detrimental to quality of the stream water due to the P linked to soil particles. PP concentrations were above the critical values of P for eutrophication during the study periods, highlighting the need to take conservation measures to reduce soil erosion and sediment delivery to watercourse.     

Phosphorus in agricultural constructed wetland sediment is sparingly plant‐available

Agricultural constructed wetlands (CWs) are intended to retain sediment and phosphorus (P) carried off with runoff and drainage water. The accumulated sediment, with adsorbed P, is often advised to be recycled to agricultural land, but little is known about the fertilizer value of sediment‐associated P. This study examined the effects on P adsorption characteristics and P plant availability of mixing CW sediment into soil. Although the total P content in the sediment was approximately equal to that in catchment soil and the NaOH‐extractable P content was higher to that in catchment soil, in adsorption‐desorption tests sediment P solubility decreased and affinity for P increased with increasing addition rate of CW sediment to soil. Already the lowest sediment addition rate (12.5% of dry weight) decreased the equilibrium P concentration (EPC₀') by 60% on average compared to unamended catchment soil. In a greenhouse pot experiment, Italian ryegrass (Lolium multiflorum L.) yield was largely unaffected by CW sediment application, but P uptake systematically decreased when the rate of sediment application to soil increased. When 12.5% dry weight of sediment was added, plant P uptake decreased by 6–50% in P‐unfertilized pots and by 6–17% in P‐fertilized pots (150 mg P kg⁻¹) compared with P uptake of ryegrass grown in unamended field soil. Our other results suggest that the plant availability of P in CW sediments is very low due to high clay content and high concentrations of aluminium (Al) and iron (Fe) (hydr)oxides in the sediment. Thus, if applied to agricultural fields in large quantities, dredged CW sediment may impair crop P supply.     

Sediment and phosphorus transfer in overland flow from a maize field receiving manure

Abstract. The transfer of suspended sediment (SS) and phosphorus (P) in overland flow from 30 m² field plots receiving either nil, surface‐applied or incorporated manure (slurry) were monitored to determine the vulnerability of land cropped to continuous forage maize to diffuse pollutant transfer in winter runoff. In the absence of slurry, P export was dominated by particulate forms, with up to 1 t SS ha^?1 and 0.75 kg total P ha^?1 collected from an individual storm event. Background concentrations of P in soluble (<0.45 μm) form were large (c. 0.5 mg L^?1) by eutrophication standards due to the previous build‐up of soil P, and largely independent of SS concentrations. Largest P exports (representing up to 23% of the slurry P applied) were measured when dairy slurry (3–13% dry solids) was surface‐applied. The P mobilized from the slurry accounted for up to 60% of total plot P export, with the majority occurring in a soluble bioavailable form during the first storm event. Initial P concentrations in runoff were in proportion to the amount of slurry P applied and significantly lower where rainfall was delayed after application. In one year, splitting the slurry application (3 × 10 kg ha^?1) reduced total P export by 25% compared to a single surface application (30 kg P ha^?1). In two years, incorporation of slurry, either by ploughing, or by tine cultivation, reduced the amount of overland flow by 50%, and the amount of P export by up to 60%, compared to the surface‐applied slurry treatments. Timeliness of slurry spreading to avoid periods of wet weather and simple cultivation of maize fields after harvest are practical and effective options to minimize SS and P transfer in land runoff from maize fields. The results also draw attention to the need to grow maize, and apply slurry to fields with a low P loss risk.     

Is mechanical soil aeration a strategy to alleviate soil compaction and decrease phosphorus and suspended sediment losses from irrigated and rain‐fed cattle‐grazed pastures?

Agriculture is a major source of phosphorus (P) and suspended sediment (SS) losses to aquatic ecosystems promoting eutrophication. Mechanical soil loosening equipments such as topsoil looseners or aerators have been reported to improve the physical quality and infiltration of soils susceptible to livestock damage resulting from treading. We hypothesized that soil aeration would significantly decrease the volume of surface runoff and consequent losses of P and SS compared with non‐aerated soil (control) in cattle‐grazed pasture on a poorly structured silt‐loam soil. Hydrologically isolated plots (2 m long × 1 m wide × 0.15 m deep) were installed in aerated and control plots to collect surface runoff following irrigation or rainfall and analysed for P and SS losses for 1 year. Soil physical properties [% macroporosity, bulk density, saturated hydraulic conductivity (K_sat) and unsaturated hydraulic conductivity (K_unsat at ?1kPa)] were measured in the aerated and control treatments and taken before each irrigation event (n = 12). Six months after mechanical aeration was employed, but before cattle grazing commenced, no significant differences in soil physical quality were found between aerated and control treatments, with the exception of a minor increase in K_unsat for the control plots. This lack of treatment difference continued after grazing and was largely attributed to the re‐settling of the poorly structured and dispersive soil. Flow‐weighted mean concentrations and annual loads of dissolved reactive P (DRP) on the mechanically aerated soil (2.24 kg DRP/ha) were approximately double those from the control treatment (1.20 kg DRP/ha). However, no significant differences were observed between treatments for surface runoff volumes and losses of total P and total SS, which may reflect the similar soil physical conditions exhibited between treatments throughout most of the trial. As observed elsewhere, time (days) since grazing or fertilizer application was found to influence P and/or SS losses. We conclude that aeration did not decrease P and SS losses. Any changes in soil physical properties such as macroporosity were short‐lived and therefore unlikely to influence surface runoff and subsequent P and SS losses for this soil type.     

Concentration Profile of Nitrogen and Phosphorus in Leachate of a Paddy Plot during the Rice Cultivation Period in Southern Korea

Abstract

The relationships between nitrogen (N) and phosphorus (P) concentrations in surface flooding water and those in the leachate of various soil depths were monitored, and temporal variation of leaching losses of N and P from a paddy plot during rice cultivation was estimated under the conditions of southern Korea. Even flooded conditions nitrification in subsurface soil was identified, but nitrate concentrations in leachate were less than 10 mg/L, the standard drinking water nitrate concentration set by the World Health Organization (WHO). The NO₃‐N and ortho‐P concentrations in the leachate were generally higher than those in the surface flooding water. Field data implied that leaching losses would not be accurately estimated under the flooded conditions of the paddy field when using the N and P concentrations of surface flooding water and infiltration depth. The leaching losses of NO₃‐N from paddy fields were high immediately after fertilization. The study results suggested that proper fertilization and irrigation strategies are required to reduce leaching losses of NO₃‐N from paddy fields.     

Sediment flow behavior in agro-watersheds of the purple soil region in China under different storm types and spatial scales

Conservation tillage has proved to be an effective option to reduce erosion and particulate phosphorus (PP) losses from fields to watercourses. However, it usually leads to the higher losses of P in dissolved reactive (DRP) form if P accumulates into the uppermost soil layer.In this study we investigated the influence of CaCO₃-rich boardmill sludge (BMS, applied 7 years ago) on soil properties and percolate quality with soil samples as well as undisturbed soil columns taken from a long-term conservation-tilled clay field experiment. A short-term laboratory experiment was undertaken to evaluate whether newly added BMS (FS) can be used to improve the quality of percolate waters by reducing turbidity, PP and DRP.The hypothesis was that BMS reduces the risk of dissolved reactive phosphorus (DRP) leaching from conservation-tilled soil. BMS served as a liming agent and counteracted the no-till-induced acidification and accumulation of DRP in the surface soil layer. Surface soil pH was on average 0.3 units higher and soil Ca 500 mg kg⁻¹ higher in the BMS-treated plots than in the plots without BMS. The ability of BMS to enhance the availability of P for plants may prevent the surface accumulation of P in NT cultivation. At the same time, BMS-induced increase in Ca and EC of the surface soil suppress the diffuse double layer by reducing P desorption and leaching risk.In the laboratory experiment, FS reduced percolate turbidity by 80% and PP and DRP concentrations by 62% and 50%, respectively. FS probably improved stability of soil aggregates in the laboratory experiment, obviously through enhanced microbial activity. The covering effect and infiltration of water through the 0–5 cm soil layer seemed to be crucial factors in reducing P losses.BMS proved to be a promising material for the applications to the conservation-tilled fields. The effect of BMS on microbes and immobilization of nutrients, should, however, be studied further in fields under a wider diversity of conditions.     

The effect of soil phosphorus on particulate phosphorus in land runoff

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg⁻¹) on the concentrations of particulate P (PP), and sorption properties (Q_max, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre⁻¹ per mg OP kg⁻¹ of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P_sat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre⁻¹) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre⁻¹, respectively). When OP was < 100 mg kg⁻¹, P_sat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P_sat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.     

Organic amendments as a source of phosphorus: agronomic and environmental impact of different animal manures applied to an acid soil

Phosphorus (P) is a non-renewable resource highlighting the significance of developing and using alternative P sources for a sustainable agriculture. The work aims to compare the effects of different organic amendments (OA) and a mineral P fertiliser as reference on P use efficiency by the crop, and on P losses to runoff waters and eroded sediments. A two-year field trial was conducted in a Dystric Regosol with Lolium sp. Treatments were: cattle manure compost (CM), solid fraction of swine (SS) and duck (DS) slurries and triple superphosphate (TSP), each applied at 50 kg P ha^?1 year^?1. Olsen P (mg P kg^?1) increased from ≈ 19 at the beginning to ≈ 30 (TSP, CM), 45 (SS) and 62 (DS) after the experiment. Most of applied P remained in soil, between 92% (SS) and 96% (TSP), plant uptake ranged from 5% (CM) to 3.5% (TSP) and total P loss in runoff and sediments ranged between 0.2% (CM) and 4% (SS). OA increased P-use efficiency by the ryegrass crop compared with mineral P fertilizer. Composted cattle manure showed the best agronomic and environmental behaviour, simultaneously increasing P-use efficiency and decreasing P losses by runoff and erosion.     

Potential phosphorus and sediment loads from sources within a dairy farmed catchment

Phosphorus (P) losses from intensively farmed dairy pastures can impair surface water quality. One of the first steps in mitigating this loss is to determine where in a field the potential for P loss is greatest. This study compared P export in overland flow from grazed pasture with areas that receive elevated P inputs and stock traffic (e.g. gateway, water trough, stream crossing and cattle lane). Intact soil blocks were removed, simulated rainfall applied and overland flow analysed for P fractions and suspended sediment (SS). Soil bulk density, hydraulic conductivity, porosity, Olsen P and water soluble P were also measured. P loss from the sites was in the order: trough > crossing > gateway > pasture. Total P losses from the trough averaged 4.20 mg P/m² while the pasture exported 0.78 mg P/m². In addition, runoff from lane soil was measured with total P averaging 5.98 mg P/m², however the method used was different from the other soils. Using stepwise linear regression, Olsen P or H₂O-P, % bare ground and % saturation were the most commonly occurring variables to predict P loss among the sites. This suggests that locating and minimizing the size of these areas in fields has the potential to significantly decrease P loss to surface waters.     

Phosphorus and nitrogen turnover and risk of waterborne phosphorus emissions in crop rotations on a clay soil in southwest Sweden

Abstract. Nutrient losses from arable land are important contributors to eutrophication of surface waters, and phosphorus (P) and nitrogen (N) usually act together to regulate production of Cyanobacteria. Concentrations and losses of both nutrients in drainage water from pipe drains were studied and compared in 15 crop rotations on a clay soil in southwest Sweden. Special emphasis was placed on P and it was possible to evaluate critical components of the crop rotations by flow-proportional water sampling. Total P concentrations in drainage water were generally small (0.04–0.18 mg L⁻¹), but during two wetter years out of six, high P concentrations were measured following certain management practices, including ploughing-in lucerne ( Medicago sativa L.) and fertilizing in advance without incorporation into the soil to meet the needs of several subsequent crops. This resulted in average flow-weighted concentrations of total P between 0.3 and 0.7 mg L⁻¹. In crop rotations containing green manures, green fallow or leguminous leys, there was also a risk for increased P losses after these crops were ploughed in. The losses increased in the order: cash crops < dairy with grass < dairy with lucerne < monoculture with barley < organic farming with cattle slurry < stockless organic farming with green manure. P balances varied between −9 and +8 kg P ha⁻¹ and N balances between +4 and +35 kg N ha⁻¹. The balances were not related to actual leaching losses. Phosphorus losses in drainage from set-aside were 67–82% of those from cash crops grown in ploughed and P-fertilized soil at the same site, indicating a high background P loss from this clay soil.     

Effects of cover crops sown in autumn on N and P leaching

A field experiment with separately tile-drained plots was used to study the ability of oilseed radish (Rhaphanus sativus L.), as a cover crop sown after harvest of a main crop of cereals or peas, to reduce nitrogen (N) and phosphorus (P) leaching losses from a clay loam in southern Sweden over 6 years. In addition to oilseed radish in pure stand, two cover crop mixtures (hairy vetch (Vicia villosa) and rye (Secale cereale) for 3 years and oilseed radish in mixture with buckwheat (Fagopyrum esculentum) for 2 years) were tested. The cover crop plots (three replicates per treatment) were compared with unplanted plots as a control. Plots cropped with oilseed radish during autumn (August–November) had significantly smaller yearly mean N concentration in drainage water over 5 of 6 years compared with unplanted controls. Mineral N content in the soil profile in autumn was significantly less in oilseed radish plots than for control plots in all years. The cover crop mixtures of hairy vetch and rye or buckwheat and oilseed radish also showed the potential to reduce soil mineral N in autumn and N concentration in drainage water, compared with unplanted controls. The cover crops had no impact on P leaching. In conclusion, oilseed radish has the ability to reduce leaching losses of N, without increasing the risk of P leaching.     

Soil phosphorus fractions in aggregate size classes in southwestern China

The build‐up of topsoil phosphorus (P) through excess fertilizer application can increase P losses in run‐off leading to negative impacts on aquatic ecosystems. To better understand the risk of P losses, the fractions of soil P in four aggregate size classes were quantified for two vegetable production sites (<10 and >25 yrs) and a conservation buffer site (8 yrs) in southwestern China. Sequential extraction methods of inorganic P (Pi) and organic P (Po) were carried out on samples from Nitisol and Gleysol soils from 0 to 5 cm and 5 to 10 cm depths. On average, soil Pi concentrations exceeded Po concentrations threefold, primarily in the bioavailable Pi fractions (labile Pi, loosely bound Pi and non‐occluded Pi). Soil Po fractions and bioavailable Pi fractions were significantly greater under the >25 yrs field than in the <10 yrs field. The conversion of fields under vegetable production to forested buffer substantially decreased the levels of the bioavailable Pi and labile Po in the Gleysol after 8 yrs. Soil macro‐aggregates (>0.25 mm) had greater concentrations of bioavailable Pi fractions and of labile and moderately labile Po than did micro‐aggregates and silt and clay size components. Although more P was stored in recalcitrant P forms, a larger percentage of all P fractions was found in macro‐aggregates in these soils. Small active P‐enriched aggregates potentially intensify export of P from the vegetable soils by run‐off, and therefore, management practices must be optimized to enhance agricultural P efficiencies.     

Soil erosion under simulated rainfall in relation to phenological stages of soybeans and tillage methods in Lages, SC, Brazil

Soil tillage may increase vulnerability to water erosion, whereas no tillage and other conservation cultivation techniques are viewed as strategies to control soil erosion. The objective of this research was to quantify runoff and soil losses by water erosion under different soil tillage systems at the Santa Catarina Highlands, southern Brazil. A field study was carried out using a rotating-boom rainfall simulator with 64 mm h⁻¹ rainfall intensity on a Typic Hapludox, between April 2003 and May 2004. Five rainfall tests were applied along successive cropstages. Surface cover was none (fallow) or soybean (Glycine max, L.). Five treatments were investigated, replicated twice. These treatments were conventional tillage on bare soil (BS) as a control treatment and the following treatments under soybean: conventional tillage (CT), no tillage over burnt crop residues on never before cultivated land (NT-B), no tillage over desiccated crop residues, also on never before cultivated land (NT-D) and traditional no tillage over desiccated crop residues on a soil tilled 4 years before this experiment (NT-PT). Water losses by surface runoff seemed to be more influenced by vegetative crop stadium than by tillage system and consequently a wide range of variation in surface runoff was found, following successive cropstages. The most efficient tillage system in reducing surface runoff and soil losses was no tillage, particularly the NT-PT treatment. Sediment losses were more influenced by tillage system than water losses. In the NT-B, NT-D and NT-PT treatments the rate of sediment losses along the crop vegetative cycle showed a tendency to increase from the first to the second cropstages and later to decrease from the third cropstage onwards. In the conventionally tilled treatment (CT) soil losses were greater than in any of the no tillage treatments (NT-D, NT-B and NT-PT) during the initial growth periods, but at the end of the vegetative period differences in sediment rates between tilled and non-tilled treatments tended to be smaller. In the BS control treatment, soil losses progressively increased following the vegetative growth season of soybean.     

Factors controlling suspended sediment yield during runoff events in small headwater catchments of the Basque Country

For the first time in the Basque Country, turbidity (NTU), discharge (l/s) and precipitation (mm) have been continuously monitored in the gauging stations located at the outlet of three catchments (Aixola, Barrendiola and Añarbe) since October 2003. In this study, several data sets derived from flood events were used to develop turbidity and suspended sediment relationships for the three catchments separately, and so to estimate continuous suspended sediment concentration (SSC). Linear relationships are found in Barrendiola and Añarbe, and two curvilinear relationships for Aixola owing to changing sediment sources in the catchment. Several event (discharge, precipitation and suspended sediment concentration) and pre-event (discharge and precipitation) factors are calculated for all the events registered. With them correlation matrixes were developed for each catchment. Although some differences are found between catchments good correlation between precipitation (P), discharge (Q) and suspended sediment (SS) variables is found in general. Pre-event conditions are also well correlated with Q and SS variables in Barrendiola (higher regulation capacity) and Añarbe (larger area) but not in Aixola (“flash floods”). SSC-discharge evolutions through the events were also analysed. For Aixola four different types of hysteretic loops were observed: single lined, clockwise, counter-clockwise and eight-shaped; while for Barrendiola and Añarbe just clockwise loops were observed.     

Runoff,sediment and nutrient losses from various tillage systems of cotton

Runoff, sediment and nutrient losses were studied from 3 tillage systems of cotton (Gossypium hirsutum L. ‘McNair 235’): (1) no-till without a cover crop (NT); (2) reduced-till with a winter wheat (Triticum aestivum L. ‘Coker 747’) as a cover crop (RTC); (3) conventional-till (CT) in the Tennessee Valley of north Alabama during the 1985 growing season. Runoff samples were collected from natural rainfall events and analyzed for sediment and nutrient losses.Among the 3 tillage systems the RTC system was the most effective in reducing the surface runoff, sediment and nutrient losses while maintaining comparable crop yield. Runoff and sediment concentrations from the CT system were high during the “critical period” (from planting to the last cultivation of the CT system). During the “non-critical period” (between the last cultivation of the CT system to harvesting) sediment concentrations from all tillage systems were relatively low even with high-runoff events. Summer cultivations reduced both surface runoff and sediment concentrations from the CT system. This may signify that a combination of conservation tillage and summer cultivation has the potential for controlling weeds without enhancing soil erosion.Concentration of ammonium nitrogen (NH₄-N) and soluble-phosphorus concentration in surface runoff were higher than the recommended standard level for public water supplies and the growth of algae, respectively. Concentration of nitrate nitrogen (NO₃-N) in the surface runoff was well within the upper limit for drinking water.     

Phosphorus Source Effects on Soil Organic Phosphorus: A 31P NMR Study

The nature of organic phosphorus (P_o) in animal waste and in soil is important from both plant nutrition and environmental perspectives. The objectives of this study were (1) to monitor the nature of P_o in different animal wastes and biosolids using solution state ³¹P NMR spectroscopy and (2) to understand the nature of P_o as affected by crop P removal in soil amended with different animal wastes and biosolids under greenhouse conditions. Two types of stockpiled cattle (Bos taurus) manure (CM1 and CM2), solid turkey (Meleagris gallopava) litter (TL), solid hog (Sus scrofa) manure (HM), and aerobically digested biosolids (SS) were used. Two kg of Wabash silt loam soil was amended with 0 or 150 mg P kg^?1 from the P sources. Seven harvests of corn (Zea mays L.) were collected, each 35 days after sowing. Organic P was extracted with 0.4 M NaOH from soil samples collected before cropping and after the seventh harvest, as well as from each P source. ³¹P NMR analysis suggested that sugar phosphomonoester was present in all P sources and was the dominant constituent of both CM1 and CM2. Phosphomonoester was detected in large amounts in TL, HM, and SS. Prior to crop P removal, the application of all P sources caused the relative content of sugar phosphomonoester to be greater than the control. Crop P removal resulted in reductions in the relative content of sugar phosphodiesters and phosphodiester in CM1‐ and CM2‐amended soils, respectively. Phosphomonoester was also decreased in TL‐, HM‐, and SS‐amended soils in response to cropping.     

The effects of applied crop residues on losses of Fe, Mn, Cu and Zn in run-off from a soil prone to crusting

Tillage practices may reduce the organic matter content in near-surface soil horizons causing crust formation. Surface conditions may cause an increase in surface run-off, thus enhancing contaminant transfer of heavy metals or an acceleration in nutrient loss. This study examines the effect of applying crop residues to the surface of tilled soils on heavy metal losses by run-off. Losses in iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were analysed. Run-off and sediment yield were measured on 1 m² plots using a rainfall simulator with a constant 65 mm/h intensity. Four successive rainfall applications were performed, the first three at 25 mm each and the last at 65 mm. Added corn straw varied between 0 and 4 t/ha in the five studied treatments. After 140 mm cumulative rainfall, total heavy metal losses were as follows: Fe from 137 to 950 mg/L, Mn from 2.3 to 12.83 mg/L, Cu from 0.09 to 0.72 mg/L and Zn from 0.31 to 2.46 mg/L. Dissolved fractions were as follows: Fe from 0.014 to 0.229 mg/L, Mn from 0.034 to 1.45 mg/L, Cu from 0.002 to 0.013 mg/L and Zn from 0.02 to 0.12 mg/L. Total concentrations of the studied elements decreased exponentially due to the effect of corn straw on soil loss. However, dissolved contents of Fe and Cu scarcely varied. Significant positive linear correlations were observed between total heavy metal content and soil and sediment loss by run-off. It is concluded that the addition of straw to a soil of low fertility prevents heavy metal loss.     

Leaching of dissolved organic carbon and nitrogen under cotton farming systems in a Vertisol

Leaching with deep drainage is one of the loss pathways of carbon (C) and nitrogen (N) in cropping fields. However, field studies in irrigated row cropping systems are sparse. A 3‐year investigation on C and N leaching associated with deep drainage was overlaid on a long‐term experiment on tillage practices and crop rotations in Australia. The treatments included cotton (Gossypium hirsutum L.) monoculture and cotton–wheat (Triticum aestivum L.) or maize (Zea maize L.) rotations with maximum or minimum tillage. The deep drainage C and N concentrations at 0.6 and 1.2 m depth were measured after furrow irrigation with ceramic cup samplers during the 2014–15, 2015–16 and 2016–17 cotton seasons. Pre‐planting dissolved organic carbon (DOC) concentration in soil at 0.6–1.2 m depth during 2016–17 was 64 mg kg^?1 for maximum tilled cotton monoculture, 36 mg kg^?1 for minimum tilled cotton monoculture and 39 mg kg^?1 for cotton–wheat, and in maize and cotton subplots 51 and 41 mg kg^?1, respectively. Post‐harvest DOC values in soil were similar in all treatments (average of 32 mg DOC kg^?1). Total organic carbon (TOC) losses in deep drainage were equal to 2%–30% of TOC gained in irrigation water. Oxidized N losses in deep drainage ranged from 0.7% to 12% of applied N (260 kg ha^?1). NOx‐N concentrations in leachate under maize systems (20 mg L^?1) were up to 73% lower than those in cotton systems (75 mg L^?1). Maize sown in rotation with cotton can improve cotton yield, reduce N leaching and improve N use efficiency of subsequent cotton.